1. Field of the Invention
The present invention relates to a radiation imaging apparatus, and a method for controlling the radiation imaging apparatus. Particularly, the present invention is well adaptable to an X-ray imaging apparatus with a C-arm used in an operating room.
2. Description of the Related Art
An X-ray imaging apparatus with a C-arm used in an operating room is required to be capable of freely imaging a portion of a patient to be operated, and to be capable of executing a computed tomography (CT) with the rotation at an angle of 180 degrees. In recent years, a function has been demanded from such an imaging apparatus in which an imaging distance can be changed to be short without fixing the imaging distance for reducing the X-ray exposure to a patient and operator.
For example, in an X-ray diagnostic apparatus discussed in Japanese Patent Application Laid-Open No. 2000-116631, a multi-joint arm is coupled to an end of a C-arm to allow an X-ray planar detection device to move within the internal space of the C-arm so as to freely image a subject from a multitude of directions without sliding the C-arm. Japanese Patent Application Laid-Open No. 2000-116631 also discusses a link mechanism that movably holds the X-ray planar detection device to the C-arm.
The X-ray diagnostic apparatus discussed in Japanese Patent Application Laid-Open No. 2000-116631 can freely image the portion of a patient to be imaged, and enables CT in which the apparatus rotates at an angle of 180 degrees. However, the multi-joint arm that is linked to the end portion of the C-arm represents a problem in that it is difficult to control the multi-joint arm to position the X-ray planar detection device at the desired imaging angle. That is, when the X-ray tube is arranged to face the X-ray planar detection device, the multi-joint becomes a hindrance since it occupies a large space within the C-arm.
An X-ray diagnostic apparatus discussed in Japanese Patent Application Laid-Open No. 2002-336220 includes an X-ray tube, an X-ray detection device, a grid portion arranged on an image-receiving surface of the X-ray detection device, and an arm supporting the X-ray tube and the X-ray detection device to be capable of changing the distance between the X-ray tube and the X-ray detection device.
The X-ray diagnostic apparatus discussed in Japanese Patent Application Laid-Open No. 2002-336220 can change the distance between the X-ray source and the two-dimensional detection device without changing the imaging axis. However, when the length of the distance to be changed increases, the slide mechanism for changing the length increases, which arises a problem of substantially increasing the outer dimension of the C-arm. When the outer dimension of the C-arm increases, the apparatus is difficult to be used in an operating room having a small work area.